In order to understand the mechanisms by which natural products function in intact plants and their usefulness for mankind, it is important to continue efforts to determine the relationships between structure, function, and physiological activity. The attempt to understand such relationships unites all projects outlined in this proposal. Terpenoids, phenolics, phytoalexins, nonprotein amino acids, and antiviral proteins are of particular interest in our program as they are all known to be physiologically active in a large number of living organisms. Such genera as Hymenoxys and Gaillardia (Asteraceae) and Ferula (Apiaceae) will continue to be important for terpenoid and phenolic studies because species in these and related genera are particularly rich sources of these types of compounds. Other ongoing projects concern the function of ribosome inactivating (antiviral) proteins in Phytolacca species. Having determined that purified Phytolacca ribosomes are indeed inactivated by Phytolacca antiviral proteins in cell-free assays, we will now investigate interactions between these ribosome inactivating proteins and ribosomes in Phytolacca whole cells, in both the presence and absence of viruses. Our finding that the cactus Cephalocereus senilis exhibits a unique chemical response to fungal and bacterial attack led to the discovery that aurones represent a new class of phytoalexins (antimicrobial compounds). The molecular control of induced aurone biosynthesis in this cactus will be investigated. Arid land plants usually produce large amounts of many different types of interesting natural products, yet there are few molecular studies of such plants. Therefore phytoalexin responses of other plants adapted to arid conditions will also be investigated. Studies of nonprotein amino acids will focus on legumes and cycads since both groups are known to contain unusual amino acids and related small peptides that may be neurotoxic to man and other animals.